A common problem seen in orthopedics and sports physical therapy practice are problems involving the knee. Among those problems, the most common involve the patello-femoral surface. The patello-femoral surface is the surface between the knee cap and the femur. Commonly, the patello-femoral surface is erupted due to trauma or disease. Such cases cause two problems clinically. One problem is pain and the second is loss of range of motion of the knee. The stationary bicycle is an excellent exercise medium to promote resurfacing of the damaged patello-femoral articulation. Resurfacing is smoothing of the internal surface by mechanical means, such as the rubbing of the femur against the surface. The high speed activities of the exercycling allow for polishing of that surface, with low compression of the patello-femoral joint, thus reducing the discomfort while at the same time allowing for strengthening of the musculature crossing for the knee joint. Predominately, the musculature are the hamstrings and quadriceps muscle groups.
The limiting factor in using the exercise bicycle comes when there is also limitation of range of motion of the joint. This occurs because there is a required range of motion in order to complete a full circle of the foot pedal while keeping the foot on pedal. An individual must have approximately 109.degree. of active knee flexion in order to complete the upper end of the circle where the knee flexion is greater, and there is approximately a 79.degree. change in range of motion as they move into forward extension. By merely changing the level of the seat height, one can often increase flexion, but there is no mechanism presently available to decrease the flexion required to complete a full rotation. For example, the U.S. Pat. No. 4,509,742 to Cones, issued Apr. 9, 1985, discloses an exercise bicycle equipped with an adjustable seat and a pair of flywheels mounted on a drive shaft on opposite sides of a pump housing. Each one of a pair of foot pedals is mounted on a different one of the flywheels. A number of spaced apart mounting locations are provided on each of the flywheels for adjusting the distance between pedals on the flywheels so that the diameter of rotation of the pedals may be adjusted for person of different heights. The U.S. Pat. No. 2,641,249 to Brockman, issued June 9, 1953 discloses an adjustable foot support device for an exercising machine. The length of the crank arm may be adjusted by a sliding connection which may be secured to a wing nut. The U.S. Pat. No. 385,717 to Kibbe, issued July 10, 1888 discloses an extensible crank arm for a bicycle of the like including a crank arm comprising two parts. One end of a first part is connected pivotally to a connecting member or loop which is slideably connected to the first crank arm. A locking mechanism fixes one crank arm relative to the second such that the length of the combined crank arms can be adjusted.